Method of making ferro-manganese having over 60% manganese from waste steel mill slags and low grade natural ores



May 22, 1956 E. c. WRIGHT 2,746,857

METHOD OF MAKING FERRO-MANGANESE HAVING OVER 60% MANGANESE FROM WASTESTEEL. MILL SLAGS AND LOW GRADE NATURAL ORE-S Filed Dec. 24, 1952 SV'ISNI OQA/OUW OLLVH INVEN TOR. E dw/'n 6I Wright H/S A T TORNEYS UnitedStates Patentl METHGD F MAKING FERRO-MANGANESE HAV- ING @VER 60%MANGANESE FROM WASTE STEEL MILL SLAGS AND LW GRADE NAT- URAL GRES EdwinC. Wright, University, Ala. Application December 24, 1952, Serial No.327,748

Ciairns. (Cl. 755-24) ing a relatively high manganese content.

In the United States, there is practically no manganese ore suitable formaking high manganese alloys and over 90% of the manganese consumed herein making steel is imported.

It is known in producing steel from pig iron that carbon, silicon,manganese, phosphorus and certain other elements must be oxidized andreduced to a low level. After reaching this stage, the slag whichcontains the undesired elements is removed and the composition of thesteel is adjusted by the addition thereto of desired elements. :lt isalso known that tbe various elements to be removed from the pig iron byoxidation do not oxidize simultaneously but successively or in stages.Thus, when molten pig iron is subjected to the action of oxidizingagents such as oxygen, air, iron ore, or the like, silicon first takesthe oxygen, manganese next, then carbon and lastly phosphorus. Theseelements which form solid oxides rise to the surface of the bath andform a slag. Since there is always a preponderance of iron present (over90% of the pig iron) during the oxidation of the bath, a' considerableamount of iron is oxidized in all stages as a-mass action effect eventhough only a small amountof .iron shouldbe oxidized under equilibriumconditions until the silicon, manganese and carbon have been oxidized.-As a result, slags now produced in steel-making operationsV are con;taminated with iron oxide, and generally have'a MnO to FeO ratio seldomreaching 2 and usuallyV below l In the manufacture of steel by theBessemer, open hearth or electric furnace process approximately 90% ofthe manganese in the charge is lost in the rening slags. These slags areconsideredwaste materials and aredisposed of on slag dumps. Thecomposition of typical waste slags from various steel-making processesare shown in Table I:

with thel other constituents charge; srnelting such charge in a blastfurnace to re- ICC As a result of'this situation, the steel industryloses as much manganese in its steel-making processes asit has to supplyin the finishing of steel. The-role of manganese in steel-making is verycrucial, since it regulates and controls 'the detrimental elementsulphur.

Throughout the history of'the steel industry,l most of these and similarslags have been discarded as Waste even though their total manganesecontent per ton of steel made, is equal to or greater than the amount ofmanganese required in producing a ton of steel. The utility and'value ofa process adapted to `recover the manganese from these waste slagstherefore should be obvious when it is realized that about 600,000 tonslof manganese are required'annually to produce about 80 million tons ofsteel.

The desirability of recovering manganese fromthese waste slags and fromlean manganese ores has long been recognized and while much work hasbeen done on the problem by the United States Bureau of Mines andothers, no satisfactory process has heretofore been developed or evendescribed, so far as I know.

One object-of this invention is to provide a process or method wherebymanganese may be eiciently and economically recovered from these wasteslags and lean manganese ores by use of existingsteel mill facilitieswithout detrimentally affecting the quality of the steel being producedin such mills.

Another object is to provide a method or process Whereby aferro-manganese alloy can be produced from these Waste slags which has arelatively high (over manganese content, a manganese to iron ratio of atleast 4 to l and which has less than .20% phosphorus, by use of ex#isting steel mill facilities Without detrimentally affecting the qualityof the steel being produced by such mills.

A further object is to providea process or method by the practice ofwhich a ferro-manganese alloy can be producedfrom these waste slags andlean manganese ores, containing from 78-82%` manganese, 6-7'% carbon,1.5% maximum silicon and less than .3% phosphorus.

These andother objects that will be apparent to those skilled in thesteel-making art, I attain by the method or process described in thespecification forming part of this application.

Broadly, the method of this invention in producing a ferro-manganesealloy rich in manganese and having a Mn to Fe ratio of at least 4 tol lfrom such waste slags or 10W grade-natural ores comprises the followingthree steps: (l)` Preparing a blast furnace charge containing a quantityof these waste steel mill slags or such low grade natural oresor amixture of such slags and natural ores together of a normal blastfurnace TABLE I Analyses and quantity of ste'el m'iflVslags BessemerSlags OpenhearthV Slags Mixer Slag Y Y 4 Min.a Ladle b Runoff n Runoff.b' Runoi d Final Ladle e '11. 7l 1 l6;-10 Y 13.68 5.65 34. 30 44. 5927. 00 42.20 15. 02 24. 60 34. 21. 00 32. 80 11. 68 19. 30 -2l.- 28 YV24.45() 20. 14 Y l17:05 12.0

11.71 14. 20 9. 50 46. 85 12.120 3:11 5. 70 3. 30 8.00 l. 2D 1. 32 3. 32. 25 1.51 2. 20 3. 00 2. 57 5. 10 Lb. Slag f.. 144 150 150 28 Lb. Mnf... 18:7 V2B. 2 20.5 8.5 9.5

Si and 0.80% Mn.

cover in the resultant molten pig iron substantially al1 of METALooMPosToN 4 there is also a highA oxidic manganese content in the slagof the order of 50% or higher whereas when the ratio of MnO to FeO islow the oxidic manganese content 'of the slag also is low.

onlyrefa'ctorylwhich can b'e used, since'it withstands the veryhightemperatures which are necessary for the thorough reduction of'manganese from this slag and since the smelting of'the'se slags causesa' rapid erosion of any of The-data in the table were obtained fromcarefully 5 the common refractories `such as silica, magnesia, tirecontrolled tests -wherein a quantity of pig iron of the inclay, etc. Thegraphite lining also supplies some carbon dicated manganese content wasmelted in a high frefor reducing MnO to Mn. quency furnace, cleaned ofkish, and thereafter oxidized I have found that the surplus of lime inthe mixture by introducinggaseous oxygen below the metal surfaceholdsvpracticallyl all of the silica in the inal slag in the through asilica tube. Progressive results were noted as form of a di-calciumsilicate, whereas `most of they iron the oxidation proceeded. Thus, heatnumbers ending in oxide and MnO of the slag'are reduced to form a mantheletter A represent one series, heat numbers ending ganese richferro-manganese alloy which separates from in B a second series and heatnumbers l0 and 11 indethe slag and may be cast into useful shapes.pendent determinations. A peculiar result ofthis smelting operation isthat the Themolten pig iron so prepared and containing about di-calciumsilicate sla'g which has a ratio of over two parts 5% of manganese ispreferably transferred from the blast of lime to one part of silica,completely disintegrates upon furnace to an acid lined Bessemerconverter in which it Soliditication to a very'iine impalpable powder,most of is blownfor from about 2 to about 5 minutes; the blowwhich willpass through a 200- meshscreen. In most'of ing being. stopped before themanganese content of the the smelting operations conducted in connectionwith the molten iron drops below 0.8%. This oxidation step may testingof the method of this invention, it was found that be performed'. in ahot metal transfer ladle, a hot metal about 10% ofthe Mn was notrecovered. This Mn remixer or an acid open hearth furnace, however,since the mains trapped in the slag asa-black constituent which mayvessel-should be acid lined, I prefer to carry on such oxibe readily'separatedfrom the very fine di-calcium silicate dation step in a bottomblown acid lined Bessemer conslag by a simple screening operation. Thisblack slag-alverter. ways contains over 50% manganese and after recoveryThe critically important features of this blowing or by screening, maybe charged back into the smeltingfuroxidationlst'ep. are'to conduct theblowing inan acid lined nace in `subsequer'it heats.- The black slag ismostly a mixvessel and to limit the air or oxygen introduced into theture of manganese carbide and carbon which has a spemolten pig iron toan amount that will leave at least cie gravity similar to the mainvolume of di-calcium sili- 0.8% manganese in the molten pig iron afterthe blowing cate slag. is stopped. Table IV shows the results of twotypical smelting At the end of this oxidation step, the carbon contentcharges wherein standard ferro-manganese alloys'are obofthe molten pigiron will exceed 3%, and very little iron tained from the high manganeseslags resulting from the will have been oxidized. If the step isperformed in an second step of this process:

TABLE IV MnO Slag Reduced Weight of Various Fluxes (gram) Ratio,Analysis Metal, Analysis of Final Yield Wt. Analysis and reducing agentCaO percent Slag Max Meta] sto, Feo Mno oao Mgo can. A120, carbon sto.ysi Fe Mn sio Feo Mno wm' Remarks: Reduced with gas whole slag turned towhite powder, 18 percent black slag-82 percent grey slag (applies toboth heats).

acid lined vessel, such as an acid lined Bessemer converter, the slagwill contain no phosphorus and will be composed primarily of manganesesilicate. This high manganese slag is then skimmed or otherwiseseparated from the molten iron and employed in the third step of thismethod by which this slag is converted into a ferro-manganese alloyhaving a relatively high manganese content and a Mn to Fe ratio of atleast 4 to l.

In carrying out this third step or stage of my method I utilize asmelting furnace having a carbon or graphite lining and preferablyprovided with a bottom tap hole. I charge such furnace with a drymixture of this high manganese converter slag plus lime (CaO) in theproportion of two parts thereof to one part of SiO2 in the slag togetherwith sufficient carbon (approximately 25% as much carbon as lime) toreduce the iron and manganese. After such mixture is blended, I chargethe same into the smelting furnace and then raise the temperature of themixture to between 1600 C. and 1700c C. When the temperature reachesabout 1650 C., most of the iron and manganese are reduced to aferro-manganese alloy having less than 1.5% silicon, since most of thesilica (Si02) is held in the slag as a di-calcium silicate.

I have found that the addition of about 5% fluorspar (CaF2) and about10% of magnesia (MgO) to this mixture is very effective in increasingthe fluidity of the high calcium slag at the smelting temperature.

I have found that carbon (including graphite) is the According to themethod of this invention, a ton of 5% manganese containing molten pigiron after being oxidized sufficiently to lower the manganese contentthereof to about 0.8% will yield about 0.1085 ton of slag containingover 38% manganese (50% MnO). With such a slag, of the containedmanganese can be recovered by the third step or stage of this method.Thus it will be seen that about 75.6 pounds of manganese can berecovered from the slag of each ton of 5% manganese containing pig irontreated in accordance with the method of this invention.

In the customary method of steel-making about onehalf a ton of pig ironis used to make one ton of steel and an average of about 14 pounds ofmanganese is required for each ton of steel produced. It is thusapparent that by incorporating into the pig iron the manganese from thewaste slags and lean manganese ores and treating the pig iron soproduced in accordance with the method of this invention, more thansuflicient manganese can be recovered to supply the total manganeserequirement of normal steel production without resorting to outsidesources.

The molten pig iron from which the rich manganese slag has beenseparated during the second step of this method or process, and whichcontains at least 0.8% manganese may be profitably employed in theproduction of steel, either by the acid Bessemer, the basic open hearthor the electric furnace method. This metal should be highly desirablefor steel-making, as the quantity of slag that will be produced will beless than in standard practices and the operating time will be shorterdue to the elimination of most of the silicon which has entered the slagas silica, SiOz. The temperature of this molten iron is Very high,generally above 3000" F.

Since this molten partially blown metal is so low in silicon, it willrequire but a small lime addition in the open hearth to make a properslag. Moreover, as the temperature of 3000 F. is approximately 500higher than the temperature of the hot metal now supplied to open hearthfurnaces, the melting time in the open hearth will be greatlyaccelerated. The combined factors of low silicon and high temperaturewill make possible an increase in open hearth production of at least 25%on typical steel-making charges of 50% hot metal and 50% cold scrap. Theore addition for oxidizing the silicon in this low silicon pig iron willbe greatly reduced over that now considered necessary. As a result ofthese several factors, the open hearth slag volume will be reduced tofrom 30 to about 50% of what is now normal.

This application is a continuation-impart of my copending applicationSerial No. 158,647, filed April 28, 1950, now abandoned.

What I claim is:

l. A method of employing lean manganese-containing material such assteel mill slags and low grade ores containing from 2 to 20% manganesein the production of a ferro-manganese alloy containing at least about60% manganese, not over 7.0% carbon, not over 1.5% silicon, and not over0.30% phosphorus, which consists in supplementing a normal blast furnacecharge with a sufficient quantity of such lean manganese material as toproduce a pig iron containing in the neighborhood of 5% manganese;smelting such a charge in a blast furnace to the extent of producing pigiron containing substantially all the manganese included in the charge;blowing such pig iron while maintained at about 1650 C. and whilecontained in an acid lined vessel, with a blast containing gaseousoxygen to produce a slag on said bath rich in manganese oxide andsilica, with a manganese to iron ratio of at least 4 to 1 and with lessthan 0.05% phosphorus; removing the slag so formed from the molten bathprior to reducing the manganese content of the bath below 0.8%; chargingthe slag so removed into a carbonlined smelting furnace together withsuicient carbon to reduce the iron and manganese oxide content of suchslag, and lime in the proportion of about two parts lime to one partsilica in such slag; smelting the mixture at a temperature within therange of from about 1600 C. to 1700" C., increasing fluidity of the slagby the addition of fluorspar (CaFz), and maintaining the mixture at sucha smelting temperature until substantially all the manganese oxidecontent therein is reduced to manganese.

2. A method as defined in claim l in which smelting of the slag isaccomplished in a carbon lined smelting furnace.

3. A method as defined in claim l in which the lean manganese-containingmaterial is only steel mill slag.

4. A method as dened in claim l in which the lean manganese-containingmaterial is only low grade ore oontaining manganese within the range offrom about 2% to about 20% 5. A method as defined in claim 1 wherein thecarbon is provided for the last-mentioned smelting operation in anamount of about 25% as much carbon as lime.

References Cited inthe le of this patent UNITED STATES PATENTS 712,925Gin Nov. 4, 1902 1,846,152 Sheldon Feb. 23, 1932 1,979,753 Los@ et a1.Nov. 6, 1934 2,701,194 Deterding Feb. 1, 1955 FOREIGN PfrnsNTs 3,808Great Britain of 1885 OTHER REFERENCES Chemical Abstracts, vol. 33, 1939column 4570. The reaction of high carbon iron-manganese melts with ironoxides, iron sulde and silicates at 1300-l400.

A Comprehensive Treatise on Inorganic and Theoretical Chemistry byMellor, vol. 12, page 164. Y

1. A METHOD OF EMPLOYING LEAN MANGANESE-CONTAINING MATERIAL SUCH ASSTEEL MILL SLAGS AND LOW GRADE ORES CONTAINING FROM 2 TO 20% MANGANESEIN THE PRODUCTION OF A FERRO-MANGANESE ALLOY CONTAINING AT LEAST ABOUT60% MANGANESE, NOT OVER 7.0% CARBON, NOT OVER 1.5% SILICON, AND NOT OVER0.30% PHOSPHORUS, WHICH CONSISTS IN SUPPLEMENTING A NORMAL BLAST FURNACECHARGE WITH A SUFFICIENT QUANTITY OF SUCH LEAN MANGANESE MATERIAL AS TOPRODUCE A PIG IRON CONTAINING IN THE NEIGHBORHOOD OF 5% MANGANESE;SMELTING SUCH A CHARGE IN A BLAST FURNACE TO THE EXTENT OF PRODUCING PIGIRON CONTAINING SUBSTANTIALLY ALL THE MANGANESE INCLUDED IN THE CHARGE;BLOWING SUCH PIG IRON WHILE MAINTAINED AT ABOUT 1650* C. AND WHILECONTAINED IN AN ACID LINED VESSEL, WITH A BLAST CONTAINING GASEOUSOXYGEN TO PRODUCE A SLAG ON SAID BATH RICH IN MANGANESE OXIDE ANDSILICA, WITH A MANGANESE TO IRON RATIO OF AT LEAST 4 TO 1 AND WITH LESSTHAN 0.05% PHOSPHORUS; REMOVING THE SLAG SO FORMED FROM THE MOLTEN BATHPRIOR TO REDUCING THE MANGANESE CONTENT OF THE BATH BELOW 0.8%; CHARGINGTHE SLAG SO REMOVED INTO A CARBON-